1. Field of the Invention
The present invention relates to a magnetic toner for use in electrophotography, electrostatic printing, magnetic recording, and the like, and particularly to a magnetic color toner for these purposes.
2. Description of the Prior Art
Electrophotography is an image forming process in which; an electrostatic latent images are formed by utilizing a photoconductive material such as cadmium sulfide, polyvinylcarbazole, selenium, or zinc oxide, for instance, by affording uniform electric charge onto a photoconductive layer and subjecting the layer to image exposure; the electrostatic images thus formed are developed with a reverse-polarity charged toner; and if necessary, the toner images are transferred and fixed onto a transfer recording medium.
Electronic printing, as disclosed in German Pat. No. 1203808 and in other literature, is a printing process in which electrically charged toner particles are led onto a recording medium by utilizing electric field and are fixed on the medium.
Electrostatic recording is a process in which electrostatic latent images are formed from information signals on a dielectric layer and developed with electrically charged toner particles, and the resulting toner images are fixed.
Magnetic recording is a process in which magnetic latent images are formed similarly on a recording medium and developed with magnetic material-containing toner particles, and the resulting toner images are transferred and fixed onto a transfer recording medium.
Various techniques are known to develop these electric or magnetic latent images with toners. The techniques are roughly classified into the dry development process and the wet development process. The former is further divided into a process employing a two-component developer composed of toner particles and carrier particles and a process employing a one-component developer which does not contain carrier particles.
Prevailing techniques belonging to the process employing a two-component developer are the magnetic brush process and the cascade process, which are different from each other in the type of carrier for carrying a toner, the former employing a powder iron carrier and the letter employing a bead carrier.
There have been proposed a variety of processes which employ a one-component developer composed of a toner alone. Of these processes, many excellent processes employing a magnetic toner are in practical use, including the Magne-Dry process, which employs an electrically conductive toner; the process of DAS No. 2,704,361, which utilizes the dielectric polarization of toner particles; the process of U.S. Pat. No. 4,121,931, in which electric charge is transferred by agitation of a toner; and the process of U.S. Ser. Nos. 938,101 and 58,434 offered by the present applicant, in which toner particles are driven to fly toward latent images to develop them.
On the other hand, the purpose of recording or copying has been diversified recently and a color copying machine compact and inexpensive is looked for which is capable of forming images of different colors as required. In the one-component magnetic toners mentioned above, magnetite or ferrite has been used conventionally as the magnetic component. Its colors, being black or dark brown, is a great obstruction to the preparation of a so-called color toner, though effective for a black toner. In order to surmount this obstruction, whitening or coloring of black magnetic materials has been proposed. However, these proposed methods are not only insufficient for masking said magnetic materials and for forming an image of intended color, but also unsatisfactory in various practical characteristics of the toner for performing electrophotography, including initial state properties such as developing ability, transferability, fixability, and cleaning ability and long-term properties such as durability, environmental stability, and preservability.